Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$6.54	12.269%	$7.3424	$7.34	$7.35	$7.30
Purchase #2	$175.59	5.364%	$185.0086	$185.01	$185.00	$185.00
Purchase #3	$99.41	5.499%	$104.8766	$104.88	$104.90	$104.90
Purchase #4	$61.37	9.616%	$67.2713	$67.27	$67.25	$67.30
Purchase #5	$155.31	12.698%	$175.0313	$175.03	$175.05	$175.00
Purchase #6	$176.75	12.178%	$198.2746	$198.27	$198.25	$198.30
Purchase #7	$129.85	13.343%	$147.1759	$147.18	$147.20	$147.20
7 purchase totals =	$804.82		$884.9807	$884.98	$885.00	$885.00